丹参多酚酸盐对健康人血小板内皮型一氧化氮合酶活性的影响

目的 观察不同浓度的丹参多酚酸盐(depside salt from Salvia Miltiorrhiza)对正常人血小板内皮型一氧化氮合酶(eNOS)活性的影响.方法 采集健康人外周静脉血,用凝胶色谱柱法纯化血小板,同位素二步色谱法测定血小板eNOS的活性.将收集的血小板分别与eNOS激动剂组织胺和(或)eNOS抑制剂N-ω硝基左旋精氨酸甲酯盐酸盐(L-NAME)或不同浓度丹参多酚酸盐一起孵育30 min后测定血小板eNOS活性.结果 组织胺可以明显增加eNOS活性;L-NAME可以明显抑制基础状态下血小板eNOS活性以及组织胺刺激后eNOS活性的增加;丹参多酚酸盐在浓度0.1～10 mg/L间呈浓度依赖性增加血小板eNOS活性(P＜0.05);浓度达10 mg/L时这种刺激作用达高峰,更高浓度时St,b板eNOS活性反而逐渐降低.结论 丹参多酚酸盐在一定剂量范围(＜10 mg/L)内可以明显增加血小板eNOS活性.     

C反应蛋白抑制血小板内皮型一氧化氮合酶活性

目的研究不同浓度的纯化重组人 C 反应蛋白(rhCRP)对正常人血小板内皮型一氧化氮合酶(eNOS)活性的影响。方法取健康人外周静脉血,用凝胶色谱柱法收集血小板,用同位素二步色谱法测定血小板eNOS 的活性。将收集的血小板和组织胺、N_ω硝基左旋精氨酸甲酯盐酸盐(L-NAME)、不同浓度纯化的 rhCRP-起孵育后测定血小板 eNOS 活性。结果组织胺可以明显增加血小板 eNOS 活性;eNOS 抑制剂 L-NAME 可以明显抑制 eNOS 活性以及用组织胺刺激后的血小板 eNOS 活性增加;rhCRP 明显抑制组织胺刺激后的 eNOS 活性,且这种抑制作用呈现显著的浓度依赖性。结论 rhCRP 对正常人血小板经组织胺诱导的 eNOS 活性有显著抑制作用,这种抑制作用一定范围内呈现显著的浓度依赖性。     

C反应蛋白抑制血小板内皮型一氧化氮合酶活性

目的 研究不同浓度的纯化重组人C反应蛋白(rhCRP)对正常人血小板内皮型一氧化氮合酶(eNOS)活性的影响.方法 取健康人外周静脉血,用凝胶色谱柱法收集血小板,用同位素二步色谱法测定血小板eNOS的活性.将收集的血小板和组织胺、Nω硝基左旋精氨酸甲酯盐酸盐(L-NAME)、不同浓度纯化的rhCRP一起孵育后测定血小板eNOS活性.结果 组织胺可以明显增加血小板eNOS活性;eNOS抑制剂L-NAME可以明显抑制eNOS活性以及用组织胺刺激后的血小板eNOS活性增加;rhCRP明显抑制组织胺刺激后的eNOS活性,且这种抑制作用呈现显著的浓度依赖性.结论 rhCRP对正常人血小板经组织胺诱导的eNOS活性有显著抑制作用,这种抑制作用一定范围内呈现显著的浓度依赖性.     

17β-雌二醇对人脐静脉内皮细胞内皮型一氧化氮合酶和一氧化氮的影响

背景门静脉高压时门静脉系统血管内皮广泛受损,除压力增高、血流冲击等因素外,体液因子的变化也是重要损伤因素之一.目的研究雌激素对人脐静脉内皮细胞(HUVEC)内皮型一氧化氮合酶(eNOS)和一氧化氮(NO)的影响,探讨其在门静脉高压血管内皮病变中的意义.方法以不同浓度17β-雌二醇和雌激素受体拮抗剂他莫昔芬单独或联合作用于体外培养的HUVEC,检测eNOS活性和NO含量变化.结果与对照组相比,1×10-9～1×10-7 mol/L 17β-雌二醇均可增加HUVEC eNOS活性,提高NO含量;1×10-8～1×10-6 mol/L他莫昔芬对HUVEC eNOS活性和NO含量均无明显影响;1×10-7 mol/L 17β-雌二醇对经1×10-6 mol/L他莫昔芬预处理的HUVEC eNOS活性和NO含量无明显影响.结论17β-雌二醇可显著增加HUVEC eNOS活性,提高NO含量,他莫昔芬则可阻断其作用.门静脉高压血管内皮病变的形成与雌激素的作用有一定关系.     

丹参多酚酸盐对高糖诱导的人脐静脉内皮细胞损伤的保护作用

目的探讨丹参多酚酸盐对体外高糖诱导人脐静脉内皮细胞损伤的保护作用及机制。方法将人脐静脉内皮细胞株分别培养在含5.5mmol/L葡萄糖(正常对照组)、30mmol/L葡萄糖(高糖损伤组)、30mmol/L葡萄糖±50mg/L丹参多酚酸盐(低剂量丹参多酚酸盐组)和30mmol/L葡萄糖±100mg/L丹参多酚酸盐(中剂量丹参多酚酸盐组)、30mmol/L葡萄糖 200mg/L丹参多酚酸盐(高剂量丹参多酚酸盐组)的培养基中培养48h,倒置相差显微镜观察细胞形态,并分别进行细胞活力、细胞培养上清液丙二醛含量、谷胱甘肽-过氧化物酶活力、一氧化氮和内皮素1分泌量的测定。结果高糖损伤组及低、中、高剂量丹参多酚酸盐组的细胞活力、丙二醛含量、谷胱甘肽-过氧化物酶活力、一氧化氮及内皮素1的分泌量与正常对照组比差异均有统计学意义(P<0.01);低、中、高剂量丹参多酚酸盐组的细胞活力、丙二醛含量、谷胱甘肽-过氧化物酶活力、一氧化氮及内皮素1的分泌量与高糖损伤组比差异均有统计学意义(P<0.01)。结论丹参多酚酸盐对体外高糖诱导的内皮细胞损伤具有保护作用,其作用机制可能通过保护细胞线粒体、清除活性氧、提高内皮细胞抗氧化酶体系的活力和抑制内皮素1的分泌而实现的。     

糖基化终产物对正常人血小板内皮型一氧化氮合酶活性及其表达的影响

目的 通过观察糖基化终产物（AGEs)对血小板内皮型一氧化氮合酶（eNOS)活性及其表达的影响，探讨AGEs损伤血小板的机制。方法 健康成人6例，取外周静脉血，用凝胶色谱柱法收集纯化的血小板悬液，分别与三种浓度的AGEs(100μg/ml,200μg/ml，400μg/ml）孵充300min，部分血小板用位素二步色谱法测定血小板一氧化氮合酶（NOS）活性；部分血小板用免疫沉淀法制备经eNOS蛋白，蛋白印迹法检测eNOS蛋白表达水平，结果 AGEs明显抑制正常人血小板NOS纯化eNOS蛋白，蛋白印迹法检测eNOS蛋白表达水平。结果 AGEs明显抑制正常人血小板NOS活性且呈浓度依赖性。正常人血小板表达eNOS；AGEs干预30min不影响eNOS表达水平。结论 AGEs通过抑制血小板eNOS活性而激活血小板，这种作用不是通过降低血小板eNOS表达实现的。     

小葱葱白提取物对人脐静脉内皮细胞一氧化氮及一氧化氮合酶的影响

目的观察小葱葱白提取物对人脐静脉内皮细胞(HUVECs)分泌一氧化氮(NO)和内皮型一氧化氮合酶(eNOS)的影响,探讨其对HUVECs血管活性分子分泌的调节作用。方法从小葱葱白中提取活性成分,体外培养HUVECs用不同浓度(100g/L,50g/L,25g/L,12.5g/L)的葱白提取物分别作用于HUVECs。观察细胞形态,MTT法观察葱白提取物对HUVECs活性的影响,比色法测定各组的NO含量,RT-PCR法及Western Blot法测定内皮型eNOS的表达水平。结果和对照组比较,小葱葱白提取物对内皮细胞形态和活性无明显影响,能增加HUVECs释放NO及eNOS生成(P<0.05或P<0.01)。结论小葱葱白提取物可能通过增加eNOS生成而提高HUVECs释放NO,从而保护内皮功能。     

植物雌激素α-玉米赤霉醇内皮依赖性舒张效应的机制研究

目的探讨植物雌激素α-玉米赤霉醇(α-ZAL)对大鼠胸主动脉环内皮依赖性舒张效应中一氧化氮合酶(NOS)-NO-环磷酸鸟苷(cGMP)系统的作用。方法采用体外血管环灌流的方法,先用10-6mol/L苯肾上腺素预收缩血管。观察10-10～10-5mol/L6个不同浓度α-ZAL对内皮完整和去除内皮的大鼠胸主动脉环的舒张作用。α-ZAL10-10～10-8mol/L为低浓度组,α-ZAL10-7～10-5mol/L为高浓度组,0.1%乙醇浓度为对照组。在高浓度组中分别预先加用10-5mol/L左旋硝基精氨酸甲酯(L-NAME组)和亚甲蓝(MB组)并观察其影响,测定动脉环中内皮型一氧化氮合酶(eNOS)和cGMP含量及灌流液中NO含量变化。结果L-NAME组和MB组均可减弱高浓度组中α-ZAL的内皮依赖性胸主动脉环舒张作用(P<0.05,P<0.01);与对照组比较,高浓度组胸主动脉环中eNOS、cGMP含量及灌流液中NO含量增高(P<0.05,P<0.01);与高浓度组比较,L-NAME组可降低灌流液中NO含量及胸主动脉环中cGMP含量(P<0.05,P<0.01);MB组可降低胸主动脉环中cGMP含量(P<0.01)。结论α-ZAL的内皮依赖性舒张作用与NOS-NO-cGMP系统的激活有关。     

前列腺素EI对人脐静脉内皮细胞中NO和eNOS的影响

目的探讨前列腺素EI(prostaglandin EI,PGEI)对内皮细胞一氧化氮(NO)表达和内皮型一氧化氮合酶(eNOS)活性的影响。方法以人脐静脉内皮细胞(HUVEC)为实验对象,检测不同浓度PGEI作用不同时间后,细胞培养上清液和细胞中NO水平的变化,以及细胞eNOS活性的改变。结果(1)随着PGEI浓度的升高,eNOS的活性和NO的含量均逐渐增加(P<0.05);(2)短时间PGEI的干预对eNOS和NO的影响均不明显,24h后细胞中eNOS活性明显升高(P<0.05),NO的含量自12h起随时间延长而增加(P<0.05);(3)用不同PGEI浓度预处理,使TNF-α对eNOS活动的抑制作用减弱。结论PGEI可能通过诱导eNOS的表达,促进NO的释放,且可以重新激活被TNF-α抑制的eNOS活性。     

他汀对NO缺乏性高血压大鼠主动脉重构的作用

目的观察他汀类药物对NO缺乏性高血压大鼠主动脉重构的作用,并探讨其可能作用机制. 方法给予大鼠L-NAME(50 mg*kg-1*d-1,L组)造成NO缺乏性高血压模型,并在该模型上同时给予西立伐他汀(0.1 mg.kg-1*d-1,L+C组)或辛伐他汀(辛伐他汀5 mg*kg-1*d-1,L+S组)干预.8周后,测定主动脉管壁面积/管腔面积(W/L)、组织一氧化氮合酶(NOS)蛋白表达和活性、脂质过氧化(MDA)水平和血清一氧化氮代谢物(NOx)水平. 结果对比正常对照组(C组),L-NAME喂养大鼠出现血压持续升高和主动脉明显重构,主动脉壁eNOS,iNOS蛋白表达及MDA水平显著增高,NOS活性低下,血清NOx水平明显降低(P均<0.01),然而未对血脂造成明显影响(P=NS);西立伐他汀和辛伐他汀在未降压和降脂的情况下,显著减轻主动脉重构,降低W/L(P均<0.01);显著抑制高血压大鼠主动脉eNOS(P分别<0.05,0.01)和iNOS过高表达(P均<0.01);同时降低组织MDA含量,提高主动脉NOS活性(P均<0.01),但未明显提高血清NOx水平(P=NS).结论他汀在未降脂和降压的情况下,减轻NO缺乏性高血压大鼠主动脉重构,这可能与其改善NO利用度和减轻氧化损害有关.     

急性冠状动脉综合征患者血小板一氧化氮合酶活性及表达改变

观察急性冠状动脉综合征患者血小板一氧化氮合酶活性及表达改变情况。急性冠状动脉综合征患者32例 ,以健康成人 2 2例作对照 ,取外周静脉血后 ,利用凝胶色谱柱法收集血小板 ,用同位素两步色谱法测定一氧化氮合酶活性 ;蛋白免疫印迹增强化学发光法检测内皮型一氧化氮合酶表达水平。结果发现 ,基础状态下血小板一氧化氮合酶活性正常人为 95 6 .0± 4 8.2pmol 10 8血小板 ,急性冠状动脉综合征患者为 5 2 5 .5± 6 0 .8pmol 10 8血小板 ,明显低于正常人 (P <0 .0 1) ,组胺刺激后血小板一氧化氮合酶活性仍低于正常对照组 (P <0 .0 1) ;与正常人相比 ,急性冠状动脉综合征患者血小板内皮型一氧化氮合酶表达无明显改变。结果提示 ,急性冠状动脉综合征患者血小板一氧化氮合酶活性降低 ,一氧化氮释放减少可能是其血小板活化的机制之一。由于血小板粘附 ,聚集白色血栓形成是急性冠状动脉综合征早期事件 ,这对我们认识冠心病发病机理、开发临床新药提供新的思路。     

丹参对脊髓损伤早期NO含量影响的实验研究

目的探讨丹参对脊髓损伤(spinal cord injury,SCI)早期防治的作用机制.方法采用新西兰大白兔32只,随机分为4组:对照组,损伤组,丹参治疗组,L-NAME(L-NG-硝基精氨酸甲酯)组,每组8只.除对照组外,其他组均按改良的Allens法致伤造成脊髓损伤模型.各组做相应处理,伤后4 h、6 h取血液标标,6 h取脊髓标本,测定血液和脊髓组织中一氧化氮(NO)的浓度,并在光镜下观察脊髓的组织形态学的变化.结果损伤组血液标本和脊髓标本NO升高,与对照组比较有统计学意义(P<0.05),丹参组血液和脊髓NO含量与对照组和L-NAME组比较无统计学意义(P>0.05).组织学形态上,伤后6 h损伤组脊髓出血坏死比较严重,大部分白质有损害,神经元细胞损害较多,而丹参组脊髓出血比较轻,大部分白质存留,神经元细胞破坏少.结论脊髓损伤后血液和脊髓组织NO的含量异常升高,丹参能降低NO浓度的异常升高,减少NO对细胞脂质膜的损害,从而保护脊髓,在一定程度上阻止继发损伤的进一步发展.     

Aspirin and clopidogrel treatment impair nitric oxide biosynthesis by platelets

Aspirin and clopidogrel are used therapeutically for their anti-platelet effects. We examined the effects of aspirin and clopidogrel on basal and β-adrenoceptor (β-AR)-mediated platelet nitric oxide (NO) synthesis in healthy subjects and patients with coronary heart disease (CHD). Healthy subjects (n = 19) were randomized in a double-blind cross-over manner to receive aspirin or clopidogrel, each at 75 mg daily, for 14 days. Patients (n = 17) of similar age with CHD, taking aspirin, were randomized double-blind to either continue on aspirin 75 mg daily or to receive clopidogrel 75 mg daily for 14 days. NO synthase (NOS) activity was measured from l-[³H]arginine to l-[³H]citrulline conversion, and cGMP was determined by radioimmunoassay, in platelets basally and following incubation with isoproterenol or albuterol (each at 10⁻⁵ mol/L). In healthy subjects, aspirin did not affect basal NOS activity or cGMP in platelets, but suppressed the normal increase in both by isoproterenol and albuterol. Clopidogrel suppressed platelet NOS activity and cGMP both basally and in response to β-AR agonists. In platelets from CHD patients, clopidogrel suppressed basal and β-AR-stimulated NOS activity and cGMP as compared with aspirin. Platelet NOS activity and cGMP were lower in CHD subjects pre-randomization compared with healthy subjects both pre-randomization and post-aspirin. We conclude that chronic aspirin treatment suppresses β-AR-stimulated but not basal platelet NO synthesis, as previously described, whereas chronic clopidogrel treatment suppresses both, with resultant functional consequences. Moreover, CHD may itself be associated with decreased platelet NO biosynthesis.     

内源性一氧化氮在哮喘大鼠气道高反应性中的作用

目的　利用一氧化氮合成前体Ｌ精氨酸（ＬＡｒｇ） 和一氧化氮合酶抑制剂亚硝基Ｌ精氨酸甲酯（ＬＮＡＭＥ）研究内源性一氧化氮在哮喘大鼠气道高反应性中的作用,探讨支气管哮喘的发病机制。方法　用卵白蛋白作为致敏原制备哮喘大鼠模型,建立大鼠离体气管环张力的测定方法,并用ＬＡｒｇ、ＬＮＡＭＥ和ＬＡｒｇ＋ ＬＮＡＭＥ孵育离体气管环,观察气管环乙酰胆碱浓度反应曲线和最大收缩反应的变化,同时观察去上皮对哮喘大鼠气道反应性的影响。结果　哮喘大鼠（１０ 只） 离体气管环经ＬＮＡＭＥ１０５ ｍｏｌ／Ｌ孵育后对乙酰胆碱的最大收缩反应从孵育前（１２４±３９） ｍｇ 上升到（１８７ ±５３） ｍｇ,孵育前、后最大收缩反应比较差异具有显著性（ Ｐ＜ ０．０１）,浓度反应曲线上移,而ＬＡｒｇ 可以逆转ＬＮＡＭＥ的作用,单用ＬＡｒｇ ２×１０５ ｍｏｌ／Ｌ和ＬＡｒｇ１０３ ｍｏｌ／Ｌ孵育气管环,对哮喘大鼠气管环的最大收缩反应和浓度反应曲线与对照组比较,差异无显著性（ Ｐ＞ ０．０５） 。去上皮哮喘大鼠气管环的反应性与上皮完整气管环比较差异有显著性（ Ｐ＜ ０．００５） ,而ＬＡｒｇ、ＬＮＡＭＥ＋ ＬＡｒｇ 和ＬＮＡＭＥ孵育去上     

Effect of IBD sera on expression of inducible and endothelial nitric oxide synthase in human umbilical vein endothelial cells

AIM: To study the expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS) and their role in inflammatory bowel disease (IBD). METHODS: We examined the effect of sera obtained from patients with active Crohn's disease (CD) and ulcerative colitis (UC) on the function and viability of human umbilical vein endothelial cells (HUVEC). HUVECs were cultured for 0-48 h in the presence of a medium containing pooled serum of healthy controls, or serum from patients with active CD or UC. Expression of eNOS and iNOS was visualized by immunofluorescence, and quantified by the densitometry of Western blots. Proliferation activity was assessed by computerized image analyses of Ki-67 immunoreactive cells, and also tested in the presence of the NOS inhibitor, 10-4 mol/ L L-NAME. Apoptosis and necrosis was examined by the annexin-V-biotin method and by propidium iodide staining, respectively. RESULTS: In HUVEC immediately after exposure to UC, serum eNOS was markedly induced, reaching a peak at 12 h. In contrast, a decrease in eNOS was observed after incubation with CD sera and the eNOS level was minimal at 20 h compared to control (18%±16% vs 23%±15% P<0.01). UC or CD serum caused a significant increase in iNOS compared to control (UC: 300%±1%; CD: 275%±7% vs 108%±4%, P<0.01). Apoptosis/ne-crosis characteristics did not differ significantly in either experiment. Increased proliferation activity was detected in the presence of CD serum or after treatment with L-NAME. Cultures showed tube-like formations after 24 h treatment with CD serum. CONCLUSION: IBD sera evoked changes in the ratio of eNOS/iNOS, whereas did not influence the viability of HUVEC. These involved down-regulation of eNOS and up-regulation of iNOS simultaneously, leading to increased proliferation activity and possibly a reduced anti-inflammatory protection of endothelial cells.     

Deficient platelet-derived nitric oxide and enhanced hemostasis in mice lacking the NOSIII gene.

Endothelial nitric oxide synthase (eNOS) has been identified in human platelets. Although platelet-derived nitric oxide (NO) has been shown to inhibit platelet recruitment in vitro, its role in the regulation of the hemostatic response in vivo has not been characterized. To define the role of platelet-derived NO in vivo, we studied mice that lacked a functional eNOS gene (NOSIII). Surface P-selectin expression in platelets from eNOS-deficient mice was not significantly altered; however, bleeding times were markedly decreased in eNOS-deficient versus wild-type mice (77.2+/-3 versus 133.4+/-3 seconds, P<0.00005). To determine the contribution of endothelium- versus platelet-derived NO to the bleeding time, isolated platelets from either eNOS-deficient or wild-type mice were transfused into a thrombocytopenic eNOS-deficient mouse and the bleeding time was measured. The bleeding times in mice transfused with eNOS-deficient platelets were significantly decreased compared with mice transfused with wild-type platelets (Deltableeding time, -24.6+/-9.1 and -3.4+/-5.3 seconds, respectively; P<0.04). Platelet recruitment was studied by measuring serotonin release from a second recruitable population of platelets that were added to stimulated platelets at the peak of NO production. There was 40.3+/-3.7% and 52. 0+/-2.1% serotonin release for platelets added to wild-type or eNOS-deficient platelets, respectively (P<0.05). In summary, mice that lacked eNOS had markedly decreased bleeding times even after endothelial NO production was controlled. These data suggest that the lack of platelet-derived NO alters in vivo hemostatic response by increasing platelet recruitment. Thus, these data support a role for platelet-derived NO production in the regulation of hemostasis.     

Membrane expression of platelet calpain

Platelet calpain has many platelet substrates, including external membrane proteins. We thus investigated whether platelet calpain II was associated with platelet membranes in unstimulated and thrombin- activated platelets. A monospecific, goat polyclonal antibody was reared to purified platelet calpain II. Sixteen whole platelet lysates were found to contain 4.5 +/- 0.7 micrograms calpain antigen II per 10(8) platelets (mean +/- SEM) as determined by a competitive enzyme- linked immunosorbent assay. Using the dipeptide fluorogenic substrate, Suc-Leu-Tyr-MCA, 17 human platelet lysates contained 3.6 +/- 0.4 micrograms calpain activity per 10(8) platelets. Platelet calpain II was associated with the Triton X-100 insoluble platelet cytoskeletons from both unstimulated and thrombin-activated platelets. When compared with the total cell content of platelet calpain II, calpain antigen (10% to 13%) and calpain activity (24% to 28%) was associated with platelet cytoskeletons in unstimulated and thrombin-activated platelets, respectively. On immunoblot, the heavy chain (80 Kd) of calpain II was detected in platelet cytoskeletons. Subcellular fractionation studies on both unstimulated and thrombin-activated platelets, revealed that half of the total platelet calpain II antigen was associated with cytosol, and the other half was associated with the membrane fraction. Platelet calpain II was not seen on the surface of unstimulated, paraformaldehyde fixed platelets by immunofluorescence. However, on thrombin-activated platelets, rim immunofluorescence was seen, indicating that activated platelets externalize their calpain. This observation was confirmed by the finding that about 2,000 molecules per platelet of an 125I-anti-calpain II Fab' specifically bound to thrombin-activated but not unstimulated platelets. Both dibucaine (1 mmol/L) and platelet activating factor (1.86 mumol/L) in the absence of external Ca++, but not collagen (5 micrograms/mL) or ionophore A23187 (2.5 mumol/L) in the absence of external Ca++, were also able to externalize platelet calpain II antigen, as indicated by a similar level of specific 125I-anti-calpain II Fab'-platelet binding. These combined studies indicate that platelet calpain II is a major protein, comprising 2% of total platelet protein, a substantial portion of which is membrane-associated. When platelets are activated by thrombin and platelet activating factor, calpain II antigen also becomes present on the external platelet surface.     

Relative importance of thrombin compared with plasmin-mediated platelet activation in response to plasminogen activation with streptokinase.

BACKGROUND. Platelet activation occurs in vivo during pharmacologic thrombolysis and may contribute to recurrent thrombosis. Plasmin does not directly activate platelets except at high concentrations; thus, the mechanisms for platelet activation during thrombolysis remain undefined. Increases in thrombin activity also occur in patients treated with fibrinolytic agents and may contribute to activation of platelets. We have shown that one mechanism for increased thrombin activity is activation of the coagulation system by plasmin. METHODS AND RESULTS. In the present study we sought to determine whether activation of platelets in response to pharmacologic activation of plasminogen in plasma is due primarily to plasmin or mediated by increased thrombin activity. Platelet-rich citrated plasma (PRP) was recalcified and incubated with 1,000 IU/ml of streptokinase or 1.0 caseinolytic units/ml of plasmin. Concentrations of fibrinopeptide A, a marker of thrombin activity, increased markedly over 10 minutes in plasma incubated with streptokinase or plasmin, but not in PRP incubated without plasminogen activator. Platelet activation characterized by the secretion of 14C-serotonin occurred within 2-4 minutes after thrombin activity increased. In stirred recalcified PRP, platelet aggregation was accelerated from 3.6 +/- 0.5 to 2.5 +/- 0.3 minutes (p less than 0.01) when incubated with 1,000 IU/ml of streptokinase. Leupeptin and aprotinin, inhibitors of plasmin activity, markedly attenuated platelet activation in response to pharmacologic activation of plasminogen. However, inhibition of thrombin with heparin, hirudin, or D-Phe-D-Pro-L-Arg-chloromethylketone was more effective in inhibiting the acceleration of platelet activation induced by plasminogen activation, despite the elaboration of plasmin activity. CONCLUSIONS. Activation of platelets during coronary thrombolysis may be due in part to increased procoagulant activity induced by plasminogen activation as well as other factors that promote platelet activation in vivo.